One of the most common methods of wire termination in connectors is hand soldering wires to a solder cup. Solder cups can be formed to match a specific wire size and are almost always formed as part of a contact pin, saving space inside a cramped connector. Unfortunately, solder cups require very careful hand soldering by skilled workers, because the heating of one cup can unsolder its neighbors. Solder cups also must be carefully arranged in the connector so as to keep their openings always facing outwards from their center. It is also very difficult to prepare solder cups in advance for termination. The assembly process requires starting in the middle of a connector and soldering the wires to the center solder cups first and slowly working out toward the outer concentric circles of solder cups. If there are any problems with joints in the middle, the rework process is very difficult. It is extraordinarily difficult to produce high quality hand soldered joints under these constraints. In addition, these carefully crafted joints must be cleaned with solvents and often mechanically brushed to remove flux residue. This leads to mechanical stress on the wires and solder joints and often causes electrical failures.
As the wires used in interconnections get smaller, the difficulties involved with using solder cups increases greatly. For example, hand soldering wires which are 0.002 inch in diameter (smaller than the diameter of a human hair) in very soft metallic materials, such as silver or copper, leads to many failures. Burned flux, oxidation, and other contaminants from soldering irons also often migrate into the joints and contaminate them. In addition, the mechanical leverage of applying a soldering iron is large and this also can lead to breakage of the fine wires during assembly. The mechanical and solvent cleaning processes also lead to breakage.